The long term objectives of the proposal are to investigate factors important in mediating blood-foreign material interactions. Specifically, they will examine (1) the effects of shear stress on adsorbed fibrinogen and circulating platelets; (2) the significance of surface-induced conformational changes of adsorbed fibrinogen with respect to platelet adhesion; and (3) the relative roles of fibrinogen and von Willebrand factor (vWF) in supporting platelet adhesion to prosthetic materials. Using a well-characterized flow cell, fibrinogen will be adsorbed from plasma to several biomaterials, including NIH reference materials, subjected to a range of shear stresses and then assayed for their ability to support platelet adhesion and to bind purified glycoprotein (GP) IIb-IIIa. Also, platelet suspensions will be sheared in a viscometer and evaluated for changes in their reactivity with adsorbed fibrinogen. Platelet adhesion to protein-coated materials will be measured with radioisotopes and an Enzyme- Linked ImmunoSorbent Assay (ELISA) technique; GP IIb-IIIa binding will be quantified with ELISA using monoclonal antibodies (Mabs) directed against the GP IIb-IIIa complex. Although resting platelets do not bind soluble fibrinogen, they do adhere to fibrinogen-coated surfaces, an interaction that may arise because of structural changes in fibrinogen resulting from adsorption to the solid surface. Hence, the status of adsorbed fibrinogen will be assayed as functions of surface chemistry and residence time on several polymeric materials by measuring the binding of purified GP IIb-IIIa and intact platelets to the adsorbed ligand. Also, the mechanism(s) by which platelets recognize adsorbed fibrinogen may differ from that when fibrinogen is in solution; this hypothesis will be explored with Mabs directed against the platelet GP IIb-IIIa receptor. Finally, the relative roles of fibrinogen and vWF in mediating platelet adhesion to prosthetic materials will be examined using human plasmas deficient in either of those two adhesive proteins. Platelet adhesion to materials coated with the deficient plasmas will be measured at shear rates ranging from 100 to 10,000 s-1. By means of such carefully controlled studies, they hope to better characterize factors governing blood-foreign material interactions.